A THC percentage and a milligram figure answer two different questions. The percentage describes concentration — THC’s share of the total weight of the material. The milligram figure describes an absolute amount — how much THC is actually present in a specific quantity of product. Comparing a percentage on one label against a milligram figure on another, without converting one into the other first, is where flower and concentrate label reading most often goes wrong.
This piece covers the conversion math only: how percentage and milligrams relate to each other, and why the product category — flower versus concentrate — changes what a given percentage means in practice. It does not cover dosing recommendations, effects, or how much of a product anyone should use.
What Concentration and Total Amount Actually Measure
THC percentage is a weight-based concentration. It describes what share of the material, by weight, is THC — independent of how much of the product is in front of you. Milligrams describe an absolute quantity: the mass of THC present in a specific amount of material.
A percentage alone cannot tell you a total amount, because it isn’t attached to a quantity. “25% THC” says nothing about milligrams until you know how many grams you’re measuring. The two figures only become comparable once you have both: concentration and weight together produce a total; either one alone does not.
A Flower Worked Example
Montana’s Department of Revenue, in consumer-facing cannabis education materials, walks through this conversion directly: a flower strain labeled at 25% THC means one gram of that flower contains 250 milligrams of THC — because 25% of 1,000 milligrams (one gram) is 250 milligrams.
The percentage stays fixed to the strain. The milligram total scales with however much of that flower is being measured: a half-gram of the same 25% flower works out to roughly 125 milligrams, not 250. The percentage doesn’t change; the milligram figure always depends on quantity.
Why Concentrates Complicate the Comparison
The same Montana materials note that concentrates and extracts run meaningfully higher in THC percentage than flower, and give a parallel example: a one-gram concentrate labeled at 80% THC contains 800 milligrams of THC — more than three times the milligram total of the 25% flower example above, for the same one-gram weight.
This is where comparing percentages across product categories becomes misleading on its own. Seeing “25%” on a flower label next to “80%” on a concentrate label is a comparison of two concentration numbers, not two amounts. Whether that percentage gap corresponds to a meaningful difference in total THC depends on how much of each product is actually being measured or used in a given instance — a figure the percentage by itself does not supply.
Why Unlike Labels Are Easy to Misread
Three pieces of information get collapsed into label numbers, and keeping them separate is the core reading skill:
- Concentration — the percentage, fixed to the product’s composition, unaffected by quantity
- Quantity — the weight of product actually being measured
- Total amount — the milligram figure, which only exists once concentration and quantity are both known
Two products can carry the same percentage and still differ substantially in total THC if their quantities differ. Two products can carry the same milligram total while having very different percentages, if one is a larger quantity of less concentrated material and the other is a smaller quantity of something more concentrated. Neither figure alone settles a comparison between two products — both numbers, for both products, are needed first.
What a Label Does Not Verify
The percentage and milligram figures printed on packaging are the seller’s stated values. The FDA notes that products that haven’t gone through its drug-approval process — which covers the large majority of cannabis and cannabis-derived consumer products on the market — have not been evaluated by the agency for proper dosage, and the agency has not determined whether the product’s effects, interactions, or potency claims hold up under review. No federal body independently confirms that a package’s printed percentage or milligram total matches what a lab would measure in that specific batch.
Potency isn’t a neutral data point to skim past, either. The CDC points to research linking products with higher THC concentrations to more severe symptoms of cannabis use disorder — one reason the percentage figure is worth reading precisely rather than treating as a marketing number.
A Quick Worksheet for Reading a Flower or Concentrate Label
When a specific label leaves you unsure what it actually tells you, working through these questions in order helps:
- What the label states — for example, a percentage figure with a net weight printed somewhere on the package
- Source: the manufacturer’s own printed label
- Limit: not independently verified by a federal regulator; may or may not match a batch-specific lab report
- Open question: does this percentage apply to the whole package, or was it measured from a sample?
- Next step: look for a batch-matched certificate of analysis and confirm it corresponds to the package in hand
- A percentage with no weight listed nearby
- Source: partial label data
- Limit: a percentage without a paired weight can’t be converted into a milligram total
- Open question: what quantity does this percentage actually apply to?
- Next step: locate the net weight elsewhere on the packaging before attempting any conversion
- Two products from different categories with different percentages
- Source: cross-category label comparison (e.g., flower vs. concentrate)
- Limit: percentage alone doesn’t indicate which product delivers more total THC in a given instance
- Open question: what quantity of each product is actually being compared?
- Next step: convert both labels to milligrams using their respective weights before comparing
If a percentage, a net weight, or a corresponding milligram total is missing from a label altogether, that’s a gap in the label — not something to estimate.
Related Reading
This page covers percentage-to-milligram conversion specifically for flower and concentrates, where weight and concentration are the relevant figures. For the equivalent math on edibles — where the relevant numbers are servings per container and milligrams per serving rather than weight and concentration — see our guide to delta-9 labels and serving math. For how a hemp-derived classification intersects with workplace policy rather than product content, see our breakdown of hemp-derived labels and workplace risk.
This article is informational only, has not been clinically or peer reviewed, and does not constitute medical or legal advice.
